The present invention relates to a thermal printing apparatus for printing on flat materials and, more particular, to thermal ribbon cassettes for use in conjunction with thermal printing apparatus.
A conventional thermal printing postage meter includes a thermal print head mounted to the registration wall of a support platform. The thermal print head is mounted to the registration wall and is aligned generally transverse to an elongated transport deck of a support platform. A platen roller which is under the influence of a drive motor is aligned opposite to the thermal print head. A thermal ribbon cassette is detachably mounted to the registration wall such that a portion of the cassette's thermal transfer ribbon is opposite the thermal print head. The indicia printing process involves positioning an envelope on the deck between the thermal cassette ribbon and the platen. The platen roller is biased to urge the printing area of the envelope against the cassette ribbon with the thermal print head providing a backing. The envelope is synchronously transporting past the thermal print head heat element array by the platen roller while a micro controller selectively actuating heating elements of the print head array. By switching a current through the selected heat elements of the thermal print head, the respective elements are heat causing the ink coating on the cassette ribbon substrate in the region of the respective element to liquefy. Due to differences in the adhesion properties between the ribbon substrate and the envelope paper, ink is transferred to the envelope print area.
In the general art of thermal printing, there are two primary types of transfer inks formulation. The first is a wax based ink formulation and the second is a polymer based ink formulation. The wax based ink formulation finds its best application where the ink is intended to be transferred to a coarse material surface. The wax base ink inhibits porous absorption of the ink and thereby enhances the contrast of the printed image. Polymer based ink formulation is best suited for application where the ink is intended to be transferred to a relatively smooth material surface. The polymer based ink inhibits diffusion absorption of the ink and thereby enhances the contrast of the printed image.
It should be appreciated that with respect to a postage indicia, it is customary for the postal authorities to specify the required indicia quality. Conventionally, thermal printing postage meters have been designed to employ a single type of transfer ink formulation. The ink formulation of choice is polymer based ink thereby restricting the envelope paper types suitable for processing by the thermal printing postage meter. Therefore, conventional applications have been restricted to a single form of ink formulation.